In a sand casting process of an internal combustion engine cylinder block, an expendable mold package is assembled from a plurality of resin-bonded sand cores (also known as mold segments) that define the internal and external surfaces of the engine block. Typically, each of the sand cores is formed by blowing resin-coated foundry sand into a core box and curing it therein.
Traditionally, the mold assembly method involves positioning a base core on a suitable surface and building up or stacking separate mold elements to shape such casting features as the sides, ends, valley, water jacket, cam openings, and crankcase. Additional cores may be present as well depending on the engine design.
Removal of thermal energy from the liquid metal in the mold package is an important consideration in the foundry process. Rapid solidification and cooling of the casting promotes a fine grain structure in the metal leading to desirable material properties such as high tensile and fatigue strength, and good machinability. For engine designs with highly stressed bulkhead features, the use of a thermal chill may be necessary. The chill is much more thermally conductive than foundry sand and readily conducts heat from those casting features it contacts. The chill typically consists of one or more steel or cast iron bodies assembled in the mold in a manner to shape some portion of the features of the casting. The chills may be placed into the base core tooling and a core formed about them, or they may be assembled into the base core or between the crankcase cores during mold assembly.
In some casting processes, metals and metal alloys are being used which differ from the metals used to form the chills. Thus, thermal expansion characteristics differ between the chills and the metal being used in the casting process. Further, the chills become larger following pouring of the metal, while the casting contracts as it cools. This results in relative movement between the metal chills and the casting.
It would be desirable to produce a mold for sand casting of engine cylinder blocks having chills wherein an expansion of a chill and a contraction of a casting caused by changes in temperature following a mold filling operation are accommodated by the chills without damage to the chill or the casting.